Prior Art
The following is a tabulation of some prior art that presently appears relevant:
Patent or Patent Application PublicationsNumberApplicant(s) or Patentee(s)DateWO0239048 (A2)PRETORIUS GERHARDUS DIRK PETRU;May 16, 2002VAN NIEKERK BECKERRU 2003127462 (A)AFANAS'EV V. A.; GEVLICH A. N.;Mar. 27, 2005TAGIROV R. M.WO 2004106840(A1)JOYNT VERNON P.Dec. 9, 2004EP1382932 (A1)MEYER HELMUTJan. 21, 2004DE19832662 (A1)HELD MANFREDFeb. 3, 2000WO2005113330 (A1)HEYWARD GEORGE; REICHARD RONALDec. 1, 2005US2004/0200347 (A1)GROSCH HERMANNOct. 14, 2004
Protection of both military and civilian vehicles, ships, aircrafts and buildings has become increasingly topical, especially in the fight against non-state combatants. During the cold war the threat to military vehicles, ships, aircrafts, buildings and installations was clearly defined in terms of industrially manufactured weapons. In war against non-state combatants, such as terrorists and insurgents, this is no longer the case. Asymmetric opponents are rarely engaging in conventional confrontations. Instead, they are trying to hit and destroy a single vehicle, ship, aircraft or building with a massive attack often by using explosives in the form of “Improvised Explosive Devises” (IEDs). Their objective is typically to harm as many people as possible in order to spread fear, gain publicity etc.
Through the ages different weapons have been used, ranging from explosives, shape charges (SC) and explosively formed projectiles (EFP). The explosives work by punching e.g. a vehicle's side or belly plate inward, and thereby harm the occupants. SC and EFP perforate e.g. a vehicle's side or belly plate and cause injury to the occupants directly.
In recent times, there has been great focus on the protection of the objects in question. The development of armor steel, ceramic, Kevlar and a wide range of composite materials has sharply reduced the effectiveness of such attacks. For attacks with explosives, in particular, the ability to maintain the vehicle's, ship's, aircraft's or building's structural integrity is crucial for the protection of the occupants. Moreover, designers have tried to distribute the effect (energy and momentum) of the attack throughout the whole structure. The response from the asymmetric opponent is therefore to increase the mass of the explosive charge. This results in an increased acceleration in the inbound direction (local acceleration) for both vehicles, ships, aircrafts or buildings surfaces facing the explosion but also in an increased global acceleration of the entire vehicle, ship, aircraft or building structure. Occupants inside those objects can therefore be harmed as a result of being impacted by the inner side of a surface or as a result of the global acceleration, which can be up till hundreds of g's (acceleration due to gravity, 9.81 m/s2). To protect the occupants against these effects, space is created to allow the surfaces to bulge inward, without impacting occupants in the object. Additionally, different materials and geometries to minimize deflection are often used as well. This may also to some extent be achieved by build-in spring-damper devices and/or crushing elements to absorb energy at a given force threshold. Regarding global acceleration, seats and floors with chock absorbing materials are often used. The object can also be designed having a shape which deflects an Incoming object or pressure wave e.g. vehicles having a V-shaped belly. Another important factor against global acceleration is the weight of the object. According to Newton's 2nd Law, acceleration is inversely proportional to the object's mass. However, having a high weight is problematic in a number of other contexts, such as cross country driving, speed and driving performance in general.
Generally, prior art has addressed the threats in three ways. Firstly, strong materials like hardened steel alloys, composites etc. have been developed in order to withstand the blast impulse from explosions as well as the penetrating capabilities of projectiles and fragments. Such materials are used as receiving bodies to shield, deflect or absorb. In cases with large quantities of energy and momentum, shielding is not enough to prevent occupant injury. In such cases, energy and momentum are mitigated in two ways in order to decrease accelerations; deflection and/or absorption. Deflection is used to prevent transfer of energy and momentum to the structure, whereas absorption is used either to absorb the energy and momentum in less critical areas of the structure or in decoupling systems like suspended seats. Deflection minimizes the forces acting on the object resulting in lower accelerations. Absorption on the other hand, minimizes the peak forces acting on an object. In principle, the impulse stays the same resulting in, that the acting forces—although having a lower peak—are stretched in time. Deflective and absorbing devises normally have rather large space claims which in most cases are not desirable for military platforms.
More novel designs like the invention described in WO0239048 (A2) mentioned above seems to overcome the issue of having a large space claim by turning the outer part of the receiving face into a deflective shield by means of the impulse generated by onboard explosives. Although, such a device may be able to mitigate global acceleration caused by the impulse from small to medium explosive charges, it is highly time critical as it has to work on a sub-millisecond time scale. The control unit must initiate the onboard explosives based on very few data samples, potentially leading to high false alarm rates. It is likely to make matters worse though with respect to local acceleration causing the belly plate to bulge even further. This is also the case in an overmatch scenario in which the onboard explosives is unable to deploy the deflecting shield because of a higher apposing impulse originating from the threat. Threats off-axis relative to the vehicle's longitudinal center axis may also cause additional lateral (horizontal) accelerations.
Another novel approach is given by the invention described in US2004/0200347 (A1) mentioned above. Energy and momentum are prevented from being transferred to critical parts of a vehicle e.g. the crew compartment by chopping off wheels and/or parts of the vehicle body. As appose to the previous invention this concept has its optimum performance when the threat is off-axis relative to the vehicle's longitudinal center axis. The blast impulse is still going to hit the critical parts of the vehicle though and only the energy and momentum transmitted through wheels and other parts hereto are omitted. However, these non-critical parts have masses too, but they no longer contribute in reducing the acceleration of say the crew compartment. In addition, the time frame for transmitting most of the energy and momentum through wheels and body parts is indeed very narrow, as this is done predominately in the form of shock waves. These in turn, are likely to tear off or shatter wheels and other body parts anyway. Hence, the system needs to be faster than the shock waves travelling through axles etc. Steel has a sonic velocity of more than 5000 m/s. For most vehicle designs this devise has to work on a sub-millisecond time scale too, giving rise to the same or similar problems as mentioned above.
Both of the above mentioned inventions suffer from the uncertainty of the threat position as well as being extremely time critical. Although they may reduce the amount of transferred energy and momentum, the predominant factor governing vehicle mine or blast protection is the mass of the vehicle as it is independent of threat position and keeps acceleration down due to any force, continuously. In both cases, at least the peak forces arising from the blast impulse acting on the vehicle or its critical parts are attempted reduced.
Although, deflecting and absorbing arrangements may have taken prior art to higher levels, they have definitely reached their limits when used on platforms of suitable size and mass for military and other purposes.